Evolution of Wireless Sensor Technologies and Energy

International Journal of Engineering Research & Technology (IJERT) Header Page 1 of 4. ISSN: 2278-0181 Vol. 2 Issue 4, April - 2013

Evolution Of Wireless Sensor Technologies And Energy Resource Management Of Microcontroller Used In Wireless Networks B N Suresh Kumar, Adapa Rajesh, Tammu Tarak RamaKrishna, Pamidi Dept. of Electrical Engineering, Blekinge Tekniska Hogskola(BTH)

Abstract—This paper is a brief survey that presents the power of 1000 cycles of CPU for one bit of data [1]. Hence, evolution of wireless sensor networks (WSN) over time and how efficient use of energy is necessary in areas of low power they are optimized and made reliable in power aspects of design. reserves. The research question of this paper is to reduce power It is to be noted that wireless sensor networks are consumption in a sensor node. Since most applications of WSNs erroneously classified as a special case of wireless ad-hoc are in areas of wilderness, power consumption is vital to make them work for long time. Microcontroller (MCU) is heart of any networks, but the truth is the algorithms and protocols used for sensor node. Now our focus is on power controlling techniques ad hoc networks are incompatible to WSNs [2]. and issues in microcontrollers. This paper describes the energy consumption techniques to reduce overall power of WSNs that are main attributes to modern day wireless technologies. It also II. PROBLEM STATEMENT AND MAIN CONTRIBUTION briefly discusses about the states of the MCU and reducing the power consumption in these states. This paper also discusses Micro controllers are employed at the core of sensor nodes about reducing the power of MCU in sleep mode via Brown out Detector (BOD). Finally, the AVR Pico power technology and which consume most of the sensor energy. We discuss about design tailored microcontrollers for application specific sensor various factors that influence the power consumption in a network node (ASIC) are also presented. MCU of a sensor. In this paper we mainly focus on various methods adapted to lessen to the power consumption of a Index Terms— Wireless sensor networking, AVR Pico power microcontroller in a sensor node. We relate the concept of technology, resource management, ASIC microcontroller, sensor AVR pico technology with MCU to reduce the total power node, Brown Out Detector. consumption of the sensor node. The concept of Application Specific Integrated Circuits (ASIC) is used so as to evolve the I. INTRODUCTION concept of tailored MCUs to reduce the power. Owing to wireless technology every corner of world is In the first section (III) the paper deals with evolution of aligned with intelligence. The evolution of wireless network WSNs and its optimization to adapt with technology demands. started as “smart dust” by Dr.Kris Pister and Co as theyIJERTIJERT In the second section (IV) the focus is how to deal with power defined it a network of microcomputers built into whatever we consumption issues in microcontrollers that used in sensor need, such as buildings, bridges and etc. The processing nodes. features such as sensing, computation and communication in III. EVOLUTION OF WSNS AND OPTIMISATION WITH small package, are right now integrated in a size of grain. TECHNOLOGY AND RELIABILITY ISSUE These nodes record information about the surroundings and send it to a neighbouring computer or to the user for A WSN can be defined as a network of devices, denoted as monitoring. These low power and relatively inexpensive tiny nodes, which can sense the environment and communicate the specs of networks can manage even a larger size city. This information gathered from the monitored field (e.g., an area or discovery of smart dust led made us to understand more about volume) through wireless links. The data is forwarded, possibly our surroundings. For example, automatic opening and closing via multiple hops, to a sink (sometimes denoted as controller or of doors by motion sensors, detecting the seismic activity by monitor) that can use it locally or connected to the other vibration sensors, automatic fire alarm by heat sensors etc. The networks (e.g. the Internet) through a gateway. [1] wireless sensor networks are a subclass of wireless ad-hoc The nodes can be stationary or moving. They can be aware networks that uses sensor nodes for sensing, communicating of their location or not. They can be homogeneous or not i.e. and computing operations that are monitored using a similar sensors node are connected to another or not networked distributed sensor network. respectively. “On one hand, WSNs enable new applications Technologies have not developed parallel and at the same and thus new possible markets, on the other hand, the design is level for all WSN components. Since the networks are powered affected by several constraints that call for new paradigms”[1]. by batteries careful monitoring has to be done to prevent out of At the end of 20th century the idea of combining MEMS service nodes. Also the radio transceiver module used for technology, Morse coding together with the communication wireless communication consumes lots of power i.e. it uses revolution gave rise to the emerging wireless sensors

www.ijert.org 175 International Journal of Engineering Research & Technology (IJERT) Header Page 2 of 4. ISSN: 2278-0181 Vol. 2 Issue 4, April - 2013 technology under the name of “dust networks” [2]. As the communicate in timeslots, similar to other TDM systems. Such reliability is the main concern of any emerging technology, it deterministic communication allows the devices to stay had taken time to achieve 99.9% reliability. Protocol reliability, extremely low power, as the radios only turn on for the periods i.e the challenges a sensor network to withstand with RF of scheduled communication. The protocol is designed to environment is main concern. It started as a single hop network operate very reliably in a noisy environment. It uses channel usually emerged as multi hop network along with some hopping to avoid interference the packets between TSMP protocols to work with it. Dust Network employs TSMP devices get sent on different radio channels depending on time [3](Time Synchronized Mesh Protocol) to keep the nodes of transmission.[7]” In addition, TSMP allows the WSN to stay awake at particular instants of time and also manage the energy in sleep mode more often than wakeful mode i.e. it has a low consumption and multi path interference in a manner that data duty cycle and the focus is then drawn to save power in sleep from no single node is dropped [2]. Also the path loss of modes. A duty cycle of a microcontroller is the percentage of various nodes in the system is calculated and it shows fair its active state in one time period. It is intuitive that a typical results [2]. In case of high path loss that interrupts data packet WSN node has a duty cycle of about < 1% because of their to be properly transferred, a mechanism to switch the operating applications. For example a temperature sensor calibrates once channel is developed. Adaptation of the operational channel in every 10 minutes, a vibration sensor placed in an earthquake based on channel quality is similar to Zigbee to Zigbee Pro prone area wakes up once in very long time. So, it is intuitive development. As the result, the described designed intelligence that its active state is very less than that of its sleep state. So in MAC (Media Access Control) or Application layers considering the power saving methods in sleep mode may constructs a reliable system. reduce overall power. Low power is dependent on many The next concern about a sensor node is physical size. In factors such as crystal oscillator frequency, temperature, the course of sensor evolution the size of a node had changed operating voltage with peripherals running. “In many from a shoe to a small grain in series of steps. In some applications, the processor does not run continuously and applications such as medicine and security the need for even peripherals may be idle much of the time. The overall power smaller size is demanded. Hence, striving is in a direction of consumption can be reduced by taking advantage of various achieving microscopic or nanoscopic sensor nodes which is the sleep modes available virtually on all processors. The most research area of future. common sleep modes are Power Down (PWD), Power Save (PS) and Idle. In Power Down mode everything is shut down, including the clock source”[4]. In Power Save mode everything IV. POWER CONSUMPTION IN MICROCONTROLLER is turned off except a 32 kHz clock running from a crystal to HIERARCHICALLY keep track of the time. Idle mode is a shallow sleep mode Fig.1 provides the intuitive understanding that in a sensor where only parts of the device are shut down but the main parts node most of the power is consumed by MCU (Micro of the microcontroller are active [4]. Controller Unit) since most of functionalities is controlled or The main consumption of power occurs in a MCU during performed by MCU its sleep mode is Brown Out Detector (BOD). BOD function is to check for the voltage levels of MCU while MCU is about to IJERTIJERTwake up. If the power is less than the required threshold level, BOD resets the device [4]. Since BOD has no functionality when the MCU is ON, a part of the power is consumed without any notable advantage. So zero power BOD is a research interest. However, reduction of the power level of BOD decreases the accuracy of analog devices. In addition, it is important to consider that the power specification on data sheets of a MCU is given without considering active peripherals. Then Atmel designed AVR Pico power technology overcomes all the described disadvantages. It has been designed to work with very low power oscillators, functional MCUs at operating voltage with an algorithm for BOD to be Fig. 1. Functional diagram of a wireless sensor. switched ON/OFF in case of requirement [4]. The next step of power saving is to design Application Specific Integrated Circuits (ASIC) to be used in WSNs. The Earliest inventions such as “smart dust” proved unreliable question that arises from a critic when named application from life time point of view since the controller is powered on specific MCU is “why to limit the usage of MCU?”. In this even when the sensor is not transmitting any data. Later the case the sensor networks have the best answer. Usually once query had been solved by novation of Time Synchronized deployed these networks work for their life time provided Mesh Protocol (TSMP)[3]. “This communications protocol for enough power sources. Hence there is no drawback in self-organizing networks of wireless devices called motes. designing ASIC for sensor networks. The main theme behind TSMP devices stay synchronized to each other and

www.ijert.org 176 International Journal of Engineering Research & Technology (IJERT) Header Page 3 of 4. ISSN: 2278-0181 Vol. 2 Issue 4, April - 2013 ASIC is to reduce the hardware utilization into a suitable level As a result, the power of flip-flops, multiplexers and etc. that according to the certain application instead of using the off the are not a part of application can be switched off according to shelf microcontrollers. A survey had been conducted among the design. The simulation shows outstanding results in a way MCUs from Atmel, TI and PIC. Among them MSP430 from TI that this design proved remarkable efficiency than MSP430 proved to be reliable and efficient than the others. The design [5]. Fig.2 and Fig.3 respectively illustrate the power of these MCU is more based on applications. According to consumption comparisons in both active and sleep mode application useless hardware is removed. After selecting the between different designs. right amount of features, MCU uses conventional low-power techniques like clock gating to reduce the dynamic power [6]. The simulation results are intuitive that the tailored Clock gating is extensively used in microcontroller design. The design of MCU yields better results than using the off the ALU (Arithmetic Logic Unit), fetch-execute pipeline, RAM, shelf MCUs. Fig 2 depicts the results in the active state of ROM, instruction decoder and program counter are all supplied microcontroller and tailored MCU always consumes less gated clock inputs to prevent unnecessary transitions and power. Fig 3 represents the sleep state power consumption and reduce dynamic power consumption. Static power, which the power consumed by tailored ASIC is less when compared becomes dominant in sleep mode [4], is improved by to other MCU’s. The simulations are done using 180nm employing low-leakage FLASH for the ROM and low-leakage CMOS technology. The present trend of CMOS technology is SRAM for RAM, as these are the largest portions of the actual 22nm CMOS technology since the technology scales 76% for hardware and consume lots of leakage power [5]. every 2-3 years[10]. Simulation using this technology could . yield far better results.

Our paper deals with only MCU power issues of a node. Since a node is made up of many other components energy management in other areas such as radio transceivers, Analog to digital converters, power sources etc is also significant. Many algorithms had been deployed till date such as PEACH[8], energy efficient clustering algorithm for data aggregation[9] etc.

V. CONCLUSION AND FUTURE WORK The vastly acceptable wireless sensor technology needs to be much more reliable in every field. The life time of the wireless node should last for long times. Many factors have influence on them. The paper discusses optimal and reliable Fig. 2. Active mode power consumption at 10Mhz in mW. employment of power levels in microcontrollers. In IJERTIJERTconclusion, as the power levels are reducing, the applications (D. Singh, S. Sai Prashanth, S. Kundu, and A. Pal, “Low-power for WSNs are in increasing trends. microcontroller for wireless sensor networks)[5] The main concern with sensor nodes of realistic size has its disadvantages in medicine, military etc. So, future work in the field of WSNs would be concentrated around building up of microscopic or nanoscopic sensor nodes with reduced power as trade off and increased reliability. Since the design of tailored MCUs yields better results than off the shelf MCUs, the hardware should be designed for ASIC MCUs. ASIC MCU can be used to reduce the size of sensor nodes. However, the disadvantage of design of tailored MCUs is that, it is asynchronous. Therefore, lot of work should be done in near future to overcome the synchronous problem, which is another important factor for power consumption.

Fig. 3. Sleep mode power consumption in uW. (D. Singh, S. Sai Prashanth, S. Kundu, and A. Pal, “Low-power microcontroller for wireless sensor networks) [5]

www.ijert.org 177 International Journal of Engineering Research & Technology (IJERT) Header Page 4 of 4. ISSN: 2278-0181 Vol. 2 Issue 4, April - 2013 VI. REFERENCES

[1] C. Buratti, A. Conti, D. Dardari, and R. Verdone, “An Overview on Wireless Sensor Networks Technology and Evolution,” Sensors (Basel), vol. 9, no. 9, pp. 6869–6896, Aug. 2009.

[2] Based on a talk by Dr.Kris Pister about “smartdust” http://www.youtube.com/watch?v=PVH1K1Eocz0 (2007)

[3] K. S. J. Pister and L. Doherty, “TSMP: Time Synchronized Mesh Protocol,” in In Proceedings of the IASTED International Symposium on Distributed Sensor Networks (DSN08, 2008)

[4] Innovative Techniques for Extremely Low Power Consumption with 8-bit Microcontrollers Arne Martin Holberg, AVR Project Manager and Asmund Saetre, AVR Marketing Manager (Atmel white paper) 2008

[5] D. Singh, S. Sai Prashanth, S. Kundu, and A. Pal, “Low-power microcontroller for wireless sensor networks,” in TENCON 2009 - 2009 IEEE Region 10 Conference, 2009, pp. 1 –6.

[6] Piguet C., Masgonty J. M., Arm C., Durand S., Schneider T., Rampogna F., Scarnera C., Iseli C., Bardyn J. P., Pache R. and Dijkstra E., “Lowpower design of 8-b embedded CoolRisc microcontroller cores.” In IEEE Journal of Solid-State Circuits, vol. 32, no. 7, Jul. 1997.

[7] Wikipedia, the free encyclopedia, http://en.wikipedia.org/wiki/TSMP, Accessed on 14 October , 2012.

[8] PEACH: Power-efficient and adaptive clustering hierarchy protocol for wireless sensor networks Sangho Yi, Junyoung Heo, Yookun Cho a, Jiman Hong b[2007] IJERTIJERT [9] Energy efficient clustering algorithm for data aggregation in wireless sensor networks SHA Chao1, WANG Ru-chuan, HUANG Hai-ping, SUN Li-juan(2010)

[10]http://en.wikipedia.org/wiki/180_nanometer[updated2012]